The present invention relates generally to a tool comprising a holding fixture for holding a workpiece and in particular to a holding fixture capable of holding a variety of workpieces having varying contours on their surfaces.
In the production of contoured parts, such as contoured panels utilized in aircraft or other large structures, it is often necessary to hold a large contoured panel in order to perform machining operations on the workpiece. Typically such machining operations comprise trimming the edge of the part to a particular shape, drilling holes for attachment of other parts of the assembly or attaching other parts directly to the workpiece. In the past, it has been necessary to fabricate an individual fixture for each workpiece to be machined. This large variety of individual holding fixtures requires a large investment in fabrication and maintenance of the work fixtures and large storage areas to store the fixtures when not in use. In addition, a substantial amount of labor is required to change the holding fixture each time a new part is to be worked on. It is, therefore, desirable to have a single fixture which is adaptable to support parts of varying contours in sizes. Such a universal holding fixture is described in U.S. Pat. No. 4,684,113.
This patent discloses a universal holding fixture equipped with plurality of workpiece holding rods which can be selectively adjusted to any height within their designed range. By individually adjusting the height of these rods in a preselected pattern, the locus of the ends of the rods forms a contoured surface adapted to the particular workpiece to be held. In the prior art devices vertical adjustment of the holding rods is critical since the end effector at the end of the rod which holds the workpiece to the rod has only a limited ability to adapt to the shape of the part. Because of the accuracy required in the height adjustment the time required to set up the fixture for a particular part is substantially increased. While this holding fixture provides substantial advantages over the prior art, it is desirable to have the holding fixture more easily adaptable to various parts thus reducing the time required for set up and tear down for each different workpiece.